Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output and a flow of exhaust gases. The exhaust gases can include a complex mixture of air pollutants produced as byproducts of the combustion process. And due to increased attention on the environment, the amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of exhaust emissions includes utilizing an exhaust gas recirculation (EGR) circuit. EGR circuits operate by recirculating a portion of the exhaust produced by the engine back to the intake of the engine to mix with fresh combustion air. The resulting mixture, when ignited, produces a lower combustion temperature and a corresponding reduced amount of regulated pollutants.
Typically, EGR circuits utilize one of the following two strategies: a donor cylinder strategy or a pumped EGR strategy. The donor cylinder strategy includes an EGR passage that receives exhaust from one or more donor cylinders, and a normal exhaust passage that extends parallel to the EGR passage. As part of the strategy, a restriction is selectively applied to the normal exhaust passage, causing more of the exhaust flow from the donor cylinders to be recirculated back to the intake of the engine. The pumped EGR strategy includes an external pump and/or compressor that draws exhaust from some of the engine cylinders and recirculates the exhaust back into the intake of the engine.
An exemplary engine implementing the donor cylinder strategy is disclosed in U.S. Patent Publication No. 2012/0000448 of Freund et al. that published on Jan. 5, 2012 (“the '448 publication”). In particular, the '448 publication discloses a diesel engine system including a group of donating cylinders and a group of non-donating cylinders. The system also includes an exhaust manifold, an exhaust gas recirculation (EGR) manifold, and one or more valve sets associated with the donating cylinders. The EGR manifold is coupled with an outlet conduit of each donating cylinder and recirculates the exhaust generated in the donating cylinders back to the donating cylinders and/or the non-donating cylinders as part of the intake air that is received by the cylinders. The valve sets direct exhaust generated by one or more of the donating cylinders between the exhaust manifold and the EGR manifold.
Although the exhaust system of the '448 publication may provide for reduced emissions in some applications, it may still be less than optimal. In particular, the use of dedicated valve sets for exhaust gas recirculation can increase the number of components in the exhaust system, resulting in an increase in cost and complexity of the engine and its associated control system.
The disclosed exhaust system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.